@import url('https://fonts.googleapis.com/css?family=Muli&display=swap');

:root{
    --line-border-fill:#3498db;
    --line-border-empty:#e0e0e0;
}

/* 初始化 */
*{
    box-sizing: border-box;
}

body{
    background-color: #f6f7fb;
    font-family: 'Muli',sans-serif;
    /* 弹性布局 水平+垂直居中 */
    display: flex;
    align-items: center;
    justify-content: center;
    height: 100vh;
    /* 溢出隐藏 */
    overflow: hidden;
    margin: 0;
}
.container{
    text-align: center;
}

.progress-container{
    display: flex;
    /* 中间有间距 */
    justify-content: space-between;
    /* 相对定位 */
    position: relative;
    margin-bottom: 30px;
    max-width: 100%;
    width: 350px;
}

.progress-container::before{
    content: "";
    background-color: var(--line-border-empty);
    /* 绝对定位 */
    position: absolute;
    top: 50%;
    left: 0;
    transform: translateY(-50%);
    height: 4px;
    width: 100%;
    z-index: -1;
}

.progress{
    background-color: var(--line-border-fill);
    position: absolute;
    top: 50%;
    left: 0;
    transform: translateY(-50%);
    height: 4px;
    width: 0%;
    z-index: -1;
    transition: 0.4s ease;
}

.circle{
    background-color: #fff;
    color: #999;
    border-radius: 50%;
    height: 30px;
    width: 30px;
     /* 弹性布局 水平+垂直居中 */
     display: flex;
     align-items: center;
     justify-content: center;
     border: 3px solid var(--line-border-empty);
     transition: 0.4s ease;
}

/* 选中状态 */
.circle.active{
    border-color: var(--line-border-fill);
}
/* 按钮 */
.btn{
    background-color: var(--line-border-fill);
    color: #FFF;
    border: 0;
    border-radius: 6px;
    /* 鼠标放上变小手 */
    cursor: pointer;
    font-family: inherit;
    padding: 8px 30px;
    margin: 5px;
    font-size: 14px;
}

/* 当按钮被点击的特效 */
.btn:active{
    transform: scale(0.98);
}

.btn:focus{
    outline: 0;
}

.btn:disabled{
    background-color: var(--line-border-empty);
    cursor: not-allowed;
}